With reference to FIGS. 1 and 2, a hydraulic system 9 of a cantilever device as disclosed in U.S. Pat. No. 7,540,457 is suitable for connecting a top support (not shown) to a bottom support (not shown) of the cantilever to a force adjustment device (not shown). The force adjustment device may be a gas spring or an oil force adjustment device. The force adjustment device 9 includes an end cap 92 that can be inserted in a base 91 and has an opening 920, an adjustment bolt 93 rotatably arranged on the end cap 92, a slider 94 having a first end 941 and a second end 942, a fixing plate 95, two bolts 96, an upper pivot 97 for pivoting the top support to the end cap 92, and a lower pivot 98 for pivoting the bottom support to the end cap 92.
The end cap 92 comprises an upper wall 921, a bottom wall 922, a stopping wall 923 that connects the upper wall 921 to the bottom wall 922, and two side walls 924 that connect the upper wall 921 to the bottom wall 922 and are located on both sides of the stopping wall 923. The edge of the upper wall 921, the edge of the bottom wall 922 and edges of the side walls 924 are jointly surrounded for defining the opening 920. The upper wall 921 has an internal surface 925 facing the bottom wall 922, an external surface 926 opposite to the internal surface 925, and a through hole 927 passing through the internal surface 925 and the external surface 926 and receiving a bolt head 931 of the adjustment bolt 93. The bottom wall 922 has a top surface 951, two joint portions 952 that are respectively located on both sides of the stopping wall 923 and protrude from the upper surface 951 toward the upper wall 921, a connecting portion 953 that are located between the joint portions 952 and protrudes from the upper surface 951 toward the upper wall 921, and a groove 954 formed in the connecting portion 953 and for receiving a distal portion 932 of the adjustment bolt 93. Each side wall 924 has an upper pivot hole 961 adjacent to the upper wall 921, and a lower pivot hole 962 adjacent to the bottom wall 922.
In assembling, the first end 941 of the slider 94 is screwed to an adjustment portion 933 of the adjustment bolt 93, and a bolt shoulder 934 of the adjustment bolt 93 is abutted against the internal surface 925 of the upper wall 921 (at this time, the end 932 of the adjustment bolt 93 is received in the groove 954 of the bottom wall 922); then the bolts 96 are respectively passed through the fixing plate 95 and are locked to the joint portions 952 of the end cap 92; then the second end 942 of the slider 94 is pivoted to one of the ends (not shown) of the force adjustment device and the other end (not shown) of the force adjustment device is pivoted to the top support; and finally the upper pivot 97 is passed through the upper pivot hole 961 of the end cap 92 and an end (not shown) of the top support, and a lower pivot 98 is passed through the lower pivot hole 962 of the end cap 92 and the end (not shown) of the bottom support. Additionally, both the other end of the top support and the other end of the bottom support are pivoted to a connector piece (not shown) that is opposite to the end cap 92 such that the preliminary assembling work of the cantilever device can be completed.
Such a hydraulic system 9 enables a user to axially move the slider 94 up and down along the direction of the adjustment bolt 93 by rotating the adjustment bolt 93. An angle between the force adjustment device and the top support is changed and thus the overall load capacity of the force adjustment device is adjusted. However, in practice, such a hydraulic system 9 has the following disadvantages:
First, in order to allow the adjustment bolt 93 to be limited within the end cap 92, the method disclosed in the above prior art adopts a design in which the end 932 of the adjustment bolt 93 is abutted against the top surface 951 of the bottom wall 922 (for preventing the adjustment bolt 93 from falling downward) and an external diameter of the bolt shoulder 934 of the adjustment bolt 93 is made to be larger than an external diameter of the bolt head 931 (for preventing the adjustment bolt 93 from falling outward from the through hole 927). Therefore, it should be appreciated that, when the user rotates the adjustment bolt 93, a feeling that the rotation is less smooth exists because the end 932 of the adjustment bolt 93 is abutted against the upper wall 921. Therefore, in general, the end 932 of the adjustment bolt 93 is additionally processed to obtain a smooth surface and is preferably designed to be tapered so as to minimize the contact area between the adjustment bolt 93 and the bottom wall 922, thereby reducing the friction force. Namely, the design of the adjustment bolt 93 and the end cap 92 of the hydraulic system 9 is sophisticated and complicated, which results in a disadvantage that the manufacturing cost cannot be reduced.
Second, the slider 94 of the hydraulic system has only one guiding bevel 943 abutting against the stopping wall 923, and the slider 94 is not limited and fixed between the side walls 924. Therefore, when the user rotates the adjustment bolt 93 to axially move the slider 94 up and down along the direction of the adjustment bolt 93, the slider 94 will shake between the side walls 924, resulting in unnecessary noise. Also, when the force adjustment device changes a free end position of the cantilever device due to external force, unnecessary abnormal friction noise may be produced between the force adjustment device and other components (such as the top support or the bottom support) as the slider 94 that connects the force adjustment device shakes. Additionally, when the force adjustment device applies force onto the slider 94 because of the angle change and then the force is transmitted to the adjustment bolt 93, the end 932 of the adjustment bolt 93 will naturally deviate toward the direction of the opening 920 due to the generation of torque which requires the hydraulic system 9 to have a fixing plate 95 to limit the end 932 of the adjustment bolt 93 to the groove 954 of the bottom wall 922.
As described above, in order to achieve a stable operation of the force adjustment device while using such a hydraulic system 9, the fitting relationship between the essential elements of the hydraulic system 9 needs to be complicated and many essential elements are required, and thus, the overall manufacturing cost cannot be reduced.